Which structure is most commonly involved in flexor tendon sheath stenosis, i.e., trigger finger?

• A. A2 pulley.
• B. A3 pulley.
• C. FDS tendon sheath.
• D. A1 pulley.

Answer: (D)

Trigger finger occurs when the pulley system that guides the flexor tendons becomes narrowed or thickened, causing the tendon to catch as the finger moves. The most common site for this stenosis is the A1 pulley, located at the level of the metacarpophalangeal joint. Thickening of the A1 pulley restricts tendon glide under the pulley, producing the characteristic catching or locking of the finger. Pulleys further along the finger, like A2 or A3, are less commonly involved in triggering and are more often linked to other pulley injuries or bowstringing, while the issue is classically described at the A1 pulley rather than the tendon sheath itself.